This invention relates generally to golf balls including a core having at least one wound layer and a cover disposed thereabout, and more particularly to wound golf balls having a wound core construction incorporating a solidified liquid material, such as a thermoplastic or thermoset polymer, therein.
Conventional golf balls can be divided into two general types or groups: solid balls and wound balls. The difference in play characteristics resulting from these different types of constructions can be quite significant.
Solid balls with a two-piece construction are generally most popular with the average recreational golfer, because they provide a very durable ball while also providing maximum distance. Two piece solid balls are made with a single solid core, usually made of a crosslinked rubber, which is encased by a hard cover material. The combination of the core and cover materials, which are very rigid, provide a hard feel for the ball when it is struck with a club and provide a ball that is virtually indestructible by golfers. This combination of materials imparts a high initial velocity to the ball, which results in improved distance. In addition, due to this combination these balls have a relatively low spin rate which provides greater distance.
At the present time, however, the wound ball remains the preferred ball of more advanced players due to its spin and feel characteristics. Wound balls typically have either a solid rubber or fluid-filled center around which many yards of a tensioned elastic thread or yam are wrapped to form a wound core. The wound core is then typically covered with a durable cover material, such as a SURLYN(copyright) or a similar material, or a softer xe2x80x9cperformancexe2x80x9d cover, such as balata or polyurethane. The cover material adheres to the wound core.
Typically, a single strand of thread is employed in forming the wound core. This thread can be wrapped at variable tension as disclosed in U.S. Pat. No. 4,783,078 issued to Giza. Some balls, however, have used two different threads of different dimensions to form the wound core. In this case, the inner most thread may be wound at a different tension and with a different pattern than the outer most thread. Furthermore, the outer most thread is generally wound in a more open pattern to form larger gaps between the thread to assure good amalgamation between the cover and the wound core.
The United States Golf Association (USGA), the organization that sets the rules of golf in the United States, has instituted a rule that prohibits the competitive use in any USGA sanctioned event of a golf ball that can achieve greater than an initial velocity of 76.2 meters per second (mis), or 250 ft/s, when tested in a standardized device operated by the USGA (referred to hereinafter as xe2x80x9cthe USGA testxe2x80x9d). An allowed tolerance of 2 percent, however, permits manufacturers to produce golf balls that achieve an initial velocity of up to 77.7 m/s (255 ft/s).
Players generally seek a golf ball that delivers maximum distance, which requires a high initial velocity upon impact. Therefore, in an effort to meet the demands of the marketplace, manufacturers strive to produce golf balls with initial velocities no greater than that permitted by the USGA test. Manufacturers try to provide these balls with a range of different properties and characteristics, such as spin and compression.
To meet the needs of golfers having varying levels of skill, golf ball manufacturers are also concerned with varying the compression of the ball, which is a measurement of the deformation of a golf ball under a fixed load. A ball with a higher compression feels harder than a ball of lower compression. With initial velocities in the range of 245 to 255 ft/sec in the USGA test, wound golf balls generally have lower compression and spin characteristics that are preferred by better players. Whether wound or solid, all golf balls become generally more resilient (i.e., have higher initial velocities) as compression increases. Manufacturers of both wound and solid construction golf balls must balance the requirement of higher initial velocity from higher compression with the desire for a softer feel from lower compression.
Wound balls typically enable a skilled golfer to have more control over the ball""s flight and final position than many non-wound balls. Particularly with approach shots into the green, the typically higher spin rate of soft covered wound balls enables the golfer to stop the ball very near its landing position. Soft covered wound balls with their lower compression, however, tend to exhibit a lower initial velocity than hard covered solid balls. This characteristic, in combination with a higher spin rate than solid balls, means wound balls generally display shorter distance than hard covered solid balls. The advantages of wound constructions over solid ones, however, are more related to spin and controllability than distance.
A softer feel is the result of a lower compression, but feel is also affected by cover hardness and thickness. In wound constructions, a thinner cover will have a softer feel, so manufacturers often strive to produce balls with the thinnest possible covers. The packing density of the windings affects the thickness of the cover, but other factors related to the cover will also affect this thickness.
Some manufacturers dip wound cores in a latex material. A light application of latex is applied to wound cores to improve cover quality or to ensure that cores or wound layers do not unravel. For example, in balls whose covers are formed in a liquid casting process, such as U.S. Pat. Nos. 5,006,297 and 5,733,428, the conventional wound cores are submerged to obtain a light application of latex material prior to covering. A xe2x80x9clight applicationxe2x80x9d of latex material is obtained with a particular combination of percentage solids applied using a particular submersion time. For a light latex application, the greater the percentage of solids, the shorter the submersion time, and when the percentage of solids decreases the submersion time can increase. For example, a light latex application can be accomplished using a latex of about 5% solids applied using a submersion time of less than eight seconds, as disclosed in U.S. Pat. No. 5,006,297. Also, a light latex application as disclosed in U.S. Pat. No. 5,733,428 is accomplished using a latex of about 30%-60% solids that is applied using a submersion time of less than eight seconds. A xe2x80x9cheavierxe2x80x9d latex application on the outer surface of the wound core reduces the amalgamation of the cover with the windings. Thus, an excessive application of latex on the outer surface of the wound core interferes with core-cover adhesion decreasing cover durability.
Another purpose of this light latex application is to seal in any air trapped between the innermost threads. If the air is not trapped, it can rise to the surface of the cover during the covering process and form air bubbles. Since these air bubbles are visible through the cover, they are undesirable imperfections in the golf ball and may result in reduced durability. As discussed above, however, a heavier application of the latex material can be problematic since it may, for example, decrease adhesion of the cover material to the wound core.
Additional references disclose other variations of a rubber or latex used with a thread layer, such as U.S. Pat. No. 4,272,079 that discloses a wound ball including a single wound thread layer over a center forming a wound core. This wound core is covered with a latex-containing ionomer resin that coats the surface of the thread layer. A cover is formed on the core. Since the latex and cover are formed with ionomer resin, an adhesive bond is formed therebetween. The ionomer latex improves the adhesion between the cover and the wound layer.
U.K. Patent No. 1,021,424 discloses a wound ball that includes a center and a rubber tape layer wound on the center. The ball further includes a first layer of rubber thread wound on the tape layer. This forms a wound core, which is immersed in a natural rubber latex that fills the interstices between the rubber threads to form a thread portion and a barrier surface on top of the thread portion. Then a second layer of thread is wound thereon. The cover is applied to the second layer of thread so that the cover penetrates the second layer of thread to the barrier surface. The barrier surface acts as a depth control for preventing the penetration of the cover material to a substantial degree inwardly towards the center. Thus, the latex material and the cover material are in contact, and the latex material effectively behaves as an extension of the cover into the thread layer.
U.S. Pat. No. 972,313 discloses a wound golf ball having a core of small rubber fragments compressed into the desired form by a rubber thread wound thereon. A layer of weighted, unvulcanized sheet rubber is disposed thereon, which includes a suitable heavy mineral powder such as red oxide of mercury. Then a second, separate layer of rubber thread is wound about the unvulcanized rubber sheet and a cover is disposed thereabout to form a golf ball.
U.K. Patent No. 1,321,269 discloses a golf ball having a spherical wound core member, a contiguous coating or thin layer of coalesced non-tacky polyurethane latex disposed about the core member, and a cover disposed about the latex layer. The latex layer is disclosed to advantageously protect the wound threads from breakage when the hot liquid cover material is applied to form the cover.
U.K. Patent No. 1,321,270 discloses a golf ball having a wound core covered by a thin plastic layer, preferably a liquid thermosetting plastic, and a cover. The thin plastic layer, or skin, penetrates the interstices of the outer thread winding of the wound layer and is on the order of 1 mil in thickness. The ball is prepared by preferably dipping a wound core as described in the preceding patent and placing the dipped, wound core in a mold, then filling the mold with a liquid curable plastics material, which is partially cured over the wound core without damaging the core. The partially cured preform is then placed in a second mold and a liquid curable plastics material is used to fill, e.g., by injection, the second mold and is partially cured to form the remainder of the cover.
Golf ball manufacturers are continually searching for new ways in which to provide wound golf balls that deliver the maximum performance for golfers. It would be advantageous to provide such a wound golf ball having improved playing characteristics.
The invention encompasses a golf ball including a center, an impregnated wound layer including a tensioned thread surrounding the center and at least one impregnation material disposed within the wound thread and having a penetration thickness greater than about 0.06 inches, and a cover including at least one layer surrounding the wound layer, wherein the thread is polymeric or glass. In another embodiment, the golf ball encompasses at least one impregnation material disposed within the wound thread and having a penetration thickness of at least about 5 percent of the thickness of the wound thread, wherein the thread is polymeric or glass.
In one embodiment, the center includes a fluid and a shell material to contain the fluid therein. In another embodiment, the wound layer has an inner edge nearer the center and an outer edge further from the center and the impregnation material is disposed adjacent the outer edge of the wound layer. In another embodiment, the impregnation material has a thickness of at least about 10 percent of the thickness of the wound thread. In another preferred embodiment, the impregnation material has a thickness of at least about 25 percent of the thickness of the wound thread. In another embodiment, the impregnation material has a thickness of at least about 50 percent of the thickness of the wound thread. In a preferred embodiment, the impregnation material penetrates substantially the entire thickness of the wound thread. In a different embodiment, which may be alternative or additional, the impregnation material has a thickness of at least about 0.1 inches, preferably with the material penetrating through at least about 10 percent of the thickness of the wound thread.
In another embodiment, the impregnation material includes materials with yield strains greater than about 10 percent. In a preferred embodiment, the yield strains are greater than about 20 percent. In a preferred embodiment, the impregnation material includes a thermoset or thermoplastic material, or a precursor thereof. In a more preferred embodiment, the impregnation material is selected from the group of vinyl resins, polyolefin homo- or co-polymers; polyurethanes; polyureas; polyamides; acrylic resins; thermoplastic rubbers; polyphenylene oxide resins; thermoplastic polyesters; solvent or suspension based latexes of polyisoprene or polybutadiene; reactive resins; and blends or mixtures thereof.
In another embodiment, the impregnated wound layer further includes at least one filler present in a sufficient amount to adjust the density of the impregnated wound layer.
In another embodiment, the golf ball includes at least one intermediate layer disposed between the impregnated wound layer and the cover. In another embodiment, the intermediate layer is adjacent to the impregnated wound layer, comprises the at least one impregnation material, and is continuous with the at least one impregnation material in the wound layer.
The invention also encompasses a method for forming a golf ball which includes forming a center, providing an impregnation material in a liquid state to a portion of a tensioned, wound thread formed of a material comprising a polymer or glass, curing the impregnation material so as to form an impregnated wound center having a substantially solid matrix material, and forming a cover on the impregnated wound center to form a golf ball.
In a preferred embodiment, the tensioned thread is wound around the center before providing the impregnation material so as to form a wound center having a wound layer disposed about the center. In a first preferred embodiment, the providing includes submerging the wound center in a liquid impregnation material, sealing the wound center and the liquid impregnation material in a cavity, and reducing the pressure sufficiently below atmospheric pressure in the sealed cavity to facilitate penetration of the impregnation material into the wound layer. In a second preferred embodiment, the providing impregnation material step includes placing the wound center in a sealed cavity, reducing the pressure in the cavity sufficiently below atmospheric pressure to facilitate penetration of the impregnation material into the wound layer, and injecting a sufficient amount of liquid impregnation material into the sealed cavity so as to penetrate and impregnate the wound layer to a desired depth. In a preferred embodiment, the pressure is reduced below about 1 Torr. In a more preferred embodiment, the pressure is reduced below about 0.01 Torr. In a third preferred embodiment, the providing step includes submerging the wound center in a liquid impregnation material, sealing the wound center and the liquid impregnation material in a cavity, increasing the pressure in the cavity sufficiently above atmospheric pressure to force the impregnation material into the voids between the wound thread to a desired penetration thickness, and then reducing the pressure to facilitate gas from the voids to escape from the wound thread. In a preferred embodiment, the increased pressure is from 1 atm to about 200 atm.
In another embodiment, the providing includes contacting a portion of the tensioned thread with a liquid impregnation material, and subsequently winding the thread around the center to form a wound center. In a preferred embodiment, the contacting process includes immersing the thread in a bath of liquid impregnation material.
In another embodiment, particularly where the impregnation material is solid at ambient temperature, the impregnation material is heated so as to remain in a liquid state before providing to the thread.
In another embodiment, the cover forming step includes compression molding, injection molding, or casting a cover material onto the impregnated wound center. In a preferred embodiment, the cover forming step is conducted by casting.